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Clewell HJ, Fuchsman PC. Interspecies scaling of toxicity reference values in human health versus ecological risk assessments: A critical review. Integr Environ Assess Manag 2024; 20:749-764. [PMID: 37724480 DOI: 10.1002/ieam.4842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Revised: 08/08/2023] [Accepted: 09/07/2023] [Indexed: 09/20/2023]
Abstract
Risk assessments that focus on anthropogenic chemicals in environmental media-whether considering human health or ecological effects-often rely on toxicity data from experimentally studied species to estimate safe exposures for species that lack similar data. Current default extrapolation approaches used in both human health risk assessments and ecological risk assessments (ERAs) account for differences in body weight between the test organisms and the species of interest, but the two default approaches differ in important ways. Human health risk assessments currently employ a default based on body weight raised to the three-quarters power. Ecological risk assessments for wildlife (i.e., mammals and birds) are typically based directly on body weight, as measured in the test organism and receptor species. This review describes differences in the experimental data underlying these default practices and discusses the many factors that affect interspecies variability in chemical exposures. The interplay of these different factors can lead to substantial departures from default expectations. Alternative methodologies for conducting more accurate interspecies extrapolations in ERAs for wildlife are discussed, including tissue-based toxicity reference values, physiologically based toxicokinetic and/or toxicodynamic modeling, chemical read-across, and a system of categorical defaults based on route of exposure and toxic mode of action. Integr Environ Assess Manag 2024;20:749-764. © 2023 SETAC.
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2
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Gentry R, Greene T, Clewell HJ, Rodricks JV. Critical considerations in the review of the toxicological evidence regarding the potential carcinogenicity of aspartame. Food Chem Toxicol 2023; 182:114105. [PMID: 37852352 DOI: 10.1016/j.fct.2023.114105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 10/13/2023] [Accepted: 10/13/2023] [Indexed: 10/20/2023]
Affiliation(s)
| | - Tracy Greene
- Ramboll US Consulting, Inc., Monroe, LA, 71201, USA
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Conolly RP, Clewell HJ, Moore MM, Campbell JL, Cheng W, Gentry RR. PBPK modeling to evaluate maximum tolerated doses: A case study with 3-chloroallyl alcohol. Front Pharmacol 2023; 14:1088011. [PMID: 36909196 PMCID: PMC9992188 DOI: 10.3389/fphar.2023.1088011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 02/09/2023] [Indexed: 02/25/2023] Open
Abstract
Introduction: A physiologically based pharmacokinetic (PBPK) model for 3-chloroallyl alcohol (3-CAA) was developed and used to evaluate the design of assays for the in vivo genotoxicity of 3-CAA. Methods: Model development was supported by read across from a published PBPK model for ethanol. Read across was motivated by the expectation that 3-CAA, which like ethanol is a primary alcohol, is metabolized largely by hepatic alcohol dehydrogenases. The PBPK model was used to evaluate how two metrics of tissue dosimetry, maximum blood concentration (Cmax; mg/L) and area under the curve (AUC; mg-hr/L) vary with dose of 3-CAA and with dose route (oral gavage, drinking water). Results: The model predicted that oral gavage results in a 6-fold higher Cmax than the same dose administered in drinking water, but in similar AUCs. Predicted Cmax provided the best correlation with severe toxicity (e.g., lethality) from 3-CAA, consistent with the production of a reactive metabolite. Therefore, drinking water administration can achieve higher sustained concentration without severe toxicity in vivo. Discussion: This evaluation is significant because cytotoxicity is a potential confounder of mutagenicity testing. The PBPK model can be used to ensure that studies meet OECD and USEPA test guidelines and that the highest dose used is not associated with severe toxicity. In addition, PBPK modeling provides assurance of target tissue (e.g., bone marrow) exposure even in the absence of laboratory data, by defining the relationship between applied dose and target tissue dose based on accepted principles of pharmacokinetics, relevant physiology and biochemistry of the dosed animals, and chemical-specific information.
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4
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Campbell JL, Clewell HJ, Van Landingham C, Gentry PR, Keene AM, Taylor MD, Andersen ME. Incorporation of rapid association/dissociation processes in tissues into the monkey and human physiologically based pharmacokinetic models for manganese. Toxicol Sci 2022; 191:212-226. [PMID: 36453847 PMCID: PMC9936208 DOI: 10.1093/toxsci/kfac123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
In earlier physiologically based pharmacokinetic (PBPK) models for manganese (Mn), the kinetics of transport of Mn into and out of tissues were primarily driven by slow rates of association and dissociation of Mn with tissue binding sites. However, Mn is known to show rapidly reversible binding in tissues. An updated Mn model for primates, following similar work with rats, was developed that included rapid association/dissociation processes with tissue Mn-binding sites, accumulation of free Mn in tissues after saturation of these Mn-binding sites and rapid rates of entry into tissues. This alternative structure successfully described Mn kinetics in tissues in monkeys exposed to Mn via various routes including oral, inhalation, and intraperitoneal, subcutaneous, or intravenous injection and whole-body kinetics and tissue levels in humans. An important contribution of this effort is showing that the extension of the rate constants for binding and cellular uptake established in the monkey were also able to describe kinetic data from humans. With a consistent model structure for monkeys and humans, there is less need to rely on cadaver data and whole-body tracer studies alone to calibrate a human model. The increased biological relevance of the Mn model structure and parameters provides greater confidence in applying the Mn PBPK models to risk assessment. This model is also well-suited to explicitly incorporate emerging information on the role of transporters in tissue disposition, intestinal uptake, and hepatobiliary excretion of Mn.
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Affiliation(s)
- Jerry L Campbell
- To whom correspondence should be addressed at Ramboll US Corporation, 3214 Charles B. Root Wynd, Suite 130, Raleigh, NC 27612, USA. E-mail:
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Conolly RB, Campbell JL, Clewell HJ, Schroeter J, Kimbell JS, Gentry PR. Relative contributions of endogenous and exogenous formaldehyde to formation of deoxyguanosine monoadducts and DNA-protein crosslink adducts of DNA in rat nasal mucosa. Toxicol Sci 2022; 191:15-24. [PMID: 36409013 PMCID: PMC9887723 DOI: 10.1093/toxsci/kfac119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Understanding the dose-response for formaldehyde-induced nasal cancer in rats is complicated by (1) the uneven distribution of inhaled formaldehyde across the interior surface of the nasal cavity and, (2) the presence of endogenous formaldehyde (endoF) in the nasal mucosa. In this work, we used computational fluid dynamics (CFD) modeling to predict flux of inhaled (exogenous) formaldehyde (exogF) from air into tissue at the specific locations where DNA adducts were measured. Experimental work has identified DNA-protein crosslink (DPX) adducts due to exogF and deoxyguanosine (DG) adducts due to both exogF and endoF. These adducts can be considered biomarkers of exposure for effects of endoF and exogF on DNA that may be part of the mechanism of tumor formation. We describe a computational model linking CFD-predicted flux of formaldehyde from air into tissue, and the intracellular production of endoF, with the formation of DPX and DG adducts. We assumed that, like exogF, endoF can produce DPX. The model accurately reproduces exogDPX, exogDG, and endoDG data after inhalation from 0.7 to 15 ppm. The dose-dependent concentrations of exogDPX and exogDG are predicted to exceed the concentrations of their endogenous counterparts at about 2 and 6 ppm exogF, respectively. At all concentrations examined, the concentrations of endoDPX and exogDPX were predicted to be at least 10-fold higher than that of their DG counterparts. The modeled dose-dependent concentrations of these adducts are suitable to be used together with data on the dose-dependence of cell proliferation to conduct quantitative modeling of formaldehyde-induced rat nasal carcinogenicity.
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Affiliation(s)
- Rory B Conolly
- To whom correspondence should be addressed at Ramboll US Consulting, Inc., 3107 Armand Street, Monroe, LA 71201, USA. E-mail:
| | | | | | - Jeffry Schroeter
- Applied Research Associates, Inc., Raleigh, North Carolina 27615, USA
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Moreau M, Mallick P, Smeltz M, Haider S, Nicolas CI, Pendse SN, Leonard JA, Linakis MW, McMullen PD, Clewell RA, Clewell HJ, Yoon M. Considerations for Improving Metabolism Predictions for In Vitro to In Vivo Extrapolation. Front Toxicol 2022; 4:894569. [PMID: 35573278 PMCID: PMC9099212 DOI: 10.3389/ftox.2022.894569] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 04/13/2022] [Indexed: 12/14/2022] Open
Abstract
High-throughput (HT) in vitro to in vivo extrapolation (IVIVE) is an integral component in new approach method (NAM)-based risk assessment paradigms, for rapidly translating in vitro toxicity assay results into the context of in vivo exposure. When coupled with rapid exposure predictions, HT-IVIVE supports the use of HT in vitro assays for risk-based chemical prioritization. However, the reliability of prioritization based on HT bioactivity data and HT-IVIVE can be limited as the domain of applicability of current HT-IVIVE is generally restricted to intrinsic clearance measured primarily in pharmaceutical compounds. Further, current approaches only consider parent chemical toxicity. These limitations occur because current state-of-the-art HT prediction tools for clearance and metabolite kinetics do not provide reliable data to support HT-IVIVE. This paper discusses current challenges in implementation of IVIVE for prioritization and risk assessment and recommends a path forward for addressing the most pressing needs and expanding the utility of IVIVE.
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Affiliation(s)
- Marjory Moreau
- ScitoVation, LLC, Durham, NC, United States
- *Correspondence: Marjory Moreau,
| | | | | | | | | | | | - Jeremy A. Leonard
- Oak Ridge Institute for Science and Education, Oak Ridge, TN, United States
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Clewell RA, Clewell HJ, Linakis M, Easley C, Langmo JN, Salley J, Gentry R, Rucker T. An in vitro approach to determine the human relevance of anti-spermatogenic effects of 4-methylmorpholine 4-oxide, monohydrate (NMMO) in rat reproductive toxicity studies. Toxicol In Vitro 2022; 82:105365. [DOI: 10.1016/j.tiv.2022.105365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 04/11/2022] [Accepted: 04/19/2022] [Indexed: 10/18/2022]
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Campbell JL, Bull RJ, Clewell HJ. Development of a rat and human PBPK model for bromate and estimation of human equivalent concentrations in drinking water. Int J Environ Health Res 2021; 31:951-962. [PMID: 31850798 DOI: 10.1080/09603123.2019.1702628] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Accepted: 12/05/2019] [Indexed: 06/10/2023]
Abstract
A physiologically based pharmacokinetic (PBPK) model was developed to described uptake, disposition and clearance of bromate in the rat using published experimental data in rat. The rodent bromate model was extrapolated to human using species-specific physiological parameters and standard interspecies scaling of rate constants. The bromate model is kinetically linear (i.e. AUC and Cmax) across the range of drinking water concentrations used in the cancer bioassays (15 to 500 ppm). This is likely the result of the poor oral bioavailability of bromate due to high reduction rates in the intestinal tract. The bromate PBPK model was used to assess the human equivalent drinking water concentration (HEC) consistent with average plasma concentrations in the rodent bioassays. At drinking water concentrations <500 mg/L, the predicted HEC was two to three fold lower than the bioassay concentration and was dependent on the reported drinking water intake reported in the bioassay.
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Efremenko A, Balbuena P, Clewell RA, Black M, Pluta L, Andersen ME, Gentry PR, Yager JW, Clewell HJ. Time-dependent genomic response in primary human uroepithelial cells exposed to arsenite for up to 60 days. Toxicology 2021; 461:152893. [PMID: 34425169 DOI: 10.1016/j.tox.2021.152893] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 07/02/2021] [Accepted: 08/05/2021] [Indexed: 11/16/2022]
Abstract
Evidence from both in vivo and in vitro studies suggests that gene expression changes from long-term exposure to arsenite evolve markedly over time, including reversals in the direction of expression change in key regulatory genes. In this study, human uroepithelial cells from the ureter segments of 4 kidney-donors were continuously treated in culture with arsenite at concentrations of 0.1 or 1 μM for 60 days. Gene expression at 10, 20, 30, 40, and 60 days was determined using Affymetrix human genome microarrays and signal pathway analysis was performed using GeneGo Metacore. Arsenic treated cells continued to proliferate for the full 60-day period, whereas untreated cells ceased proliferating after approximately 30 days. A peak in the number of gene changes in the treated cells compared to untreated controls was observed between 30 and 40 days of exposure, with substantially fewer changes at 10 and 60 days, suggesting remodeling of the cells over time. Consistent with this possibility, the direction of expression change for a number of key genes was reversed between 20 and 30 days, including CFOS and MDM2. While the progression of gene changes was different for each subject, a common pattern was observed in arsenic treated cells over time, with early upregulation of oxidative stress responses (HMOX1, NQ01, TXN, TXNRD1) and down-regulation of immune/inflammatory responses (IKKα). At around 30 days, there was a transition to increased inflammatory and proliferative signaling (AKT, CFOS), evidence of epithelial-to-mesenchymal transition (EMT), and alterations in DNA damage responses (MDM2, ATM). A common element in the changing response of cells to arsenite over time appears to involve up-regulation of MDM2 by inflammatory signaling (through AP-1 and NF-κB), leading to inhibition of P53 function.
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Affiliation(s)
- Alina Efremenko
- The Hamner Institutes for Health Sciences, RTP, NC, United States
| | | | | | - Michael Black
- The Hamner Institutes for Health Sciences, RTP, NC, United States
| | - Linda Pluta
- The Hamner Institutes for Health Sciences, RTP, NC, United States
| | | | | | - Janice W Yager
- Ramboll US Corporation, Emeryville, CA, United States(1)
| | - Harvey J Clewell
- The Hamner Institutes for Health Sciences, RTP, NC, United States.
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Andersen ME, Hagenbuch B, Apte U, Corton JC, Fletcher T, Lau C, Roth WL, Staels B, Vega GL, Clewell HJ, Longnecker MP. Why is elevation of serum cholesterol associated with exposure to perfluoroalkyl substances (PFAS) in humans? A workshop report on potential mechanisms. Toxicology 2021; 459:152845. [PMID: 34246716 PMCID: PMC9048712 DOI: 10.1016/j.tox.2021.152845] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 05/25/2021] [Accepted: 06/22/2021] [Indexed: 01/09/2023]
Abstract
Serum concentrations of cholesterol are positively correlated with exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in humans. The associated change in cholesterol is small across a broad range of exposure to PFOA and PFOS. Animal studies generally have not indicated a mechanism that would account for the association in humans. The extent to which the relationship is causal is an open question. Nonetheless, the association is of particular importance because increased serum cholesterol has been considered as an endpoint to derive a point of departure in at least one recent risk assessment. To gain insight into potential mechanisms for the association, both causal and non-causal, an expert workshop was held Oct 31 and Nov 1, 2019 to discuss relevant data and propose new studies. In this report, we summarize the relevant background data, the discussion among the attendees, and their recommendations for further research.
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Affiliation(s)
| | - Bruno Hagenbuch
- Department of Pharmacology, Toxicology & Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd - MS 1018, Kansas City, KS 66160, USA.
| | - Udayan Apte
- Department of Pharmacology, Toxicology & Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd - MS 1018, Kansas City, KS 66160, USA.
| | - J Christopher Corton
- Advanced Experimental Toxicology Models Branch, Biomolecular and Computational Toxicology Division, Center for Computational Toxicology and Exposure, US Environmental Protection Agency, 109 T.W. Alexander Dr., MD B105-03, Research Triangle Park, NC 27711, USA.
| | - Tony Fletcher
- London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
| | - Christopher Lau
- Reproductive and Developmental Toxicology Branch, Public Health and Integrated Toxicology Division, Mail Code B105-04, Center for Public Health and Environmental Assessment, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
| | - William L Roth
- U.S. Food and Drug Administration (Retired), Numerical Animals, 16005 Frontier Rd., Reno, NV 89508, USA.
| | - Bart Staels
- Univ. Lille, Inserm, CHU de Lille, Institut Pasteur de Lille, U1011-EGID, F-59019 Lille, France.
| | - Gloria L Vega
- Center for Human Nutrition, Dallas, TX, USA; Department of Clinical Nutrition, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-9052, USA.
| | - Harvey J Clewell
- Ramboll US Consulting, Inc., 3214 Charles B. Root Wynd, Suite 130, Raleigh, NC 27612, USA.
| | - Matthew P Longnecker
- Ramboll US Consulting, Inc., 3214 Charles B. Root Wynd, Suite 130, Raleigh, NC 27612, USA.
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Andersen ME, Mallick P, Clewell HJ, Yoon M, Olsen GW, Longnecker MP. Using quantitative modeling tools to assess pharmacokinetic bias in epidemiological studies showing associations between biomarkers and health outcomes at low exposures. Environ Res 2021; 197:111183. [PMID: 33887277 DOI: 10.1016/j.envres.2021.111183] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 04/07/2021] [Accepted: 04/12/2021] [Indexed: 06/12/2023]
Abstract
Biomarkers of exposure can be measured at lower and lower levels due to advances in analytical chemistry. Using these sensitive methods, some epidemiology studies report associations between biomarkers and health outcomes at biomarker levels much below those associated with effects in animal studies. While some of these low exposure associations may arise from increased sensitivity of humans compared with animals or from species-specific responses, toxicology studies with drugs, commodity chemicals and consumer products have not generally indicated significantly greater sensitivity of humans compared with test animals for most health outcomes. In some cases, these associations may be indicative of pharmacokinetic (PK) bias, i.e., a situation where a confounding factor or the health outcome itself alters pharmacokinetic processes affecting biomarker levels. Quantitative assessment of PK bias combines PK modeling and statistical methods describing outcomes across large numbers of individuals in simulated populations. Here, we first provide background on the types of PK models that can be used for assessing biomarker levels in human population and then outline a process for considering PK bias in studies intended to assess associations between biomarkers and health outcomes at low levels of exposure. After providing this background, we work through published examples where these PK methods have been applied with several chemicals/chemical classes - polychlorinated biphenyls (PCBs), perfluoroalkyl substances (PFAS), polybrominated biphenyl ethers (PBDE) and phthalates - to assess the possibility of PK bias. Studies of the health effects of low levels of exposure will be improved by developing some confidence that PK bias did not play significant roles in the observed associations.
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Mallick P, Moreau M, Song G, Efremenko AY, Pendse SN, Creek MR, Osimitz TG, Hines RN, Hinderliter P, Clewell HJ, Lake BG, Yoon M. Development and Application of a Life-Stage Physiologically Based Pharmacokinetic (PBPK) Model to the Assessment of Internal Dose of Pyrethroids in Humans. Toxicol Sci 2021; 173:86-99. [PMID: 31593217 PMCID: PMC6944222 DOI: 10.1093/toxsci/kfz211] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
To address concerns around age-related sensitivity to pyrethroids, a life-stage physiologically based pharmacokinetic (PBPK) model, supported by in vitro to in vivo extrapolation (IVIVE) was developed. The model was used to predict age-dependent changes in target tissue exposure of 8 pyrethroids; deltamethrin (DLM), cis-permethrin (CPM), trans-permethrin, esfenvalerate, cyphenothrin, cyhalothrin, cyfluthrin, and bifenthrin. A single model structure was used based on previous work in the rat. Intrinsic clearance (CLint) of each individual cytochrome P450 or carboxylesterase (CES) enzyme that are active for a given pyrethroid were measured in vitro, then biologically scaled to obtain in vivo age-specific total hepatic CLint. These IVIVE results indicate that, except for bifenthrin, CES enzymes are largely responsible for human hepatic metabolism (>50% contribution). Given the high efficiency and rapid maturation of CESs, clearance of the pyrethroids is very efficient across ages, leading to a blood flow-limited metabolism. Together with age-specific physiological parameters, in particular liver blood flow, the efficient metabolic clearance of pyrethroids across ages results in comparable to or even lower internal exposure in the target tissue (brain) in children than that in adults in response to the same level of exposure to a given pyrethroid (Cmax ratio in brain between 1- and 25-year old = 0.69, 0.93, and 0.94 for DLM, bifenthrin, and CPM, respectively). Our study demonstrated that a life-stage PBPK modeling approach, coupled with IVIVE, provides a robust framework for evaluating age-related differences in pharmacokinetics and internal target tissue exposure in humans for the pyrethroid class of chemicals.
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Affiliation(s)
| | - Marjory Moreau
- ScitoVation, LLC, Research Triangle Park, North Carolina 27709
| | - Gina Song
- ScitoVation, LLC, Research Triangle Park, North Carolina 27709.,ToxStrategies, Cary, North Carolina 27511
| | | | - Salil N Pendse
- ScitoVation, LLC, Research Triangle Park, North Carolina 27709
| | - Moire R Creek
- Moire Creek Toxicology Consulting Services, Lincoln, California 95648
| | | | - Ronald N Hines
- US EPA, ORD, NHEERL, Research Triangle Park, North Carolina 27709
| | | | | | - Brian G Lake
- Faculty of Health and Medical Sciences, University of Surrey, Surrey, UK
| | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, North Carolina 27709.,ToxStrategies, Cary, North Carolina 27511
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Thompson CM, Gentry R, Fitch S, Lu K, Clewell HJ. An updated mode of action and human relevance framework evaluation for Formaldehyde-Related nasal tumors. Crit Rev Toxicol 2021; 50:919-952. [PMID: 33599198 DOI: 10.1080/10408444.2020.1854679] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Formaldehyde is a reactive aldehyde naturally present in all plant and animal tissues and a critical component of the one-carbon metabolism pathway. It is also a high production volume chemical used in the manufacture of numerous products. Formaldehyde is also one of the most well-studied chemicals with respect to environmental fate, biology, and toxicology-including carcinogenic potential, and mode of action (MOA). In 2006, a published MOA for formaldehyde-induced nasal tumors in rats concluded that nasal tumors were most likely driven by cytotoxicity and regenerative cell proliferation, with possible contributions from direct genotoxicity. In the past 15 years, new research has better informed the MOA with the publication of in vivo genotoxicity assays, toxicogenomic analyses, and development of ultra-sensitive methods to measure endogenous and exogenous formaldehyde-induced DNA adducts. Herein, we review and update the MOA for nasal tumors, with particular emphasis on the numerous studies published since 2006. These new studies further underscore the involvement of cytotoxicity and regenerative cell proliferation, and further inform the genotoxic potential of inhaled formaldehyde. The data lend additional support for the use of mechanistic data for the derivation of toxicity criteria and/or scientifically supported approaches for low-dose extrapolation for the risk assessment of formaldehyde.
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Affiliation(s)
| | | | | | - Kun Lu
- Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, NC, USA
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Bury D, Alexander-White C, Clewell HJ, Cronin M, Desprez B, Detroyer A, Efremenko A, Firman J, Hack E, Hewitt NJ, Kenna G, Klaric M, Lester C, Mahony C, Ouedraogo G, Paini A, Schepky A. New framework for a non-animal approach adequately assures the safety of cosmetic ingredients - A case study on caffeine. Regul Toxicol Pharmacol 2021; 123:104931. [PMID: 33905778 DOI: 10.1016/j.yrtph.2021.104931] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 03/11/2021] [Accepted: 04/13/2021] [Indexed: 11/19/2022]
Abstract
This case study on the model substance caffeine demonstrates the viability of a 10-step read-across (RAX) framework in practice. New approach methodologies (NAM), including RAX and physiologically-based kinetic (PBK) modelling were used to assess the consumer safety of caffeine. Appropriate animal systemic toxicity data were used from the most relevant RAX analogue while assuming that no suitable animal toxicity data were available for caffeine. Based on structural similarities, three primary metabolites of the target chemical caffeine (theophylline, theobromine and paraxanthine) were selected as its most relevant analogues, to estimate a point of departure in order to support a next generation risk assessment (NGRA). On the basis of the pivotal mode of action (MOA) of caffeine and other methylxanthines, theophylline appeared to be the most potent and suitable analogue. A worst-case aggregate exposure assessment determined consumer exposure to caffeine from different sources, such as cosmetics and food/drinks. Using a PBK model to estimate human blood concentrations following exposure to caffeine, an acceptable Margin of Internal Exposure (MOIE) of 27-fold was derived on the basis of a RAX using theophylline animal data, which suggests that the NGRA approach for caffeine is sufficiently conservative to protect human health.
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Affiliation(s)
- Dagmar Bury
- L'Oréal, Research & Innovation, 9 Rue Pierre Dreyfus, 92110, Clichy, France.
| | - Camilla Alexander-White
- MKTox & Co Ltd, 36 Fairford Crescent, Downhead Park, Milton Keynes, Buckinghamshire, MK15 9AQ, UK
| | - Harvey J Clewell
- Ramboll Health Sciences, 3107 Armand Street, Monroe, LA, 71201, USA
| | - Mark Cronin
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 AF, UK
| | - Bertrand Desprez
- Cosmetics Europe, 40 Avenue Hermann-Debroux, 1160, Brussels, Belgium
| | - Ann Detroyer
- L'Oréal, Research & Innovation, 1 Avenue Eugène Schueller, Aulnay-sous-Bois, France
| | | | - James Firman
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Byrom Street, Liverpool, L3 AF, UK
| | - Eric Hack
- ScitoVation, Research Triangle Park, Durham, NC, USA
| | | | - Gerry Kenna
- Cosmetics Europe, 40 Avenue Hermann-Debroux, 1160, Brussels, Belgium
| | - Martina Klaric
- Cosmetics Europe, 40 Avenue Hermann-Debroux, 1160, Brussels, Belgium
| | | | | | - Gladys Ouedraogo
- L'Oréal, Research & Innovation, 1 Avenue Eugène Schueller, Aulnay-sous-Bois, France
| | - Alicia Paini
- European Commission Joint Research Centre, Ispra, Italy
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15
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Stevens AJ, Campbell JL, Travis KZ, Clewell HJ, Hinderliter PM, Botham PA, Cook AR, Minnema DJ, Wolf DC. Paraquat pharmacokinetics in primates and extrapolation to humans. Toxicol Appl Pharmacol 2021; 417:115463. [PMID: 33631232 DOI: 10.1016/j.taap.2021.115463] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 02/12/2021] [Accepted: 02/14/2021] [Indexed: 11/28/2022]
Abstract
By extending our Paraquat (PQ) work to include primates we have implemented a modelling and simulation strategy that has enabled PQ pharmacokinetic data to be integrated into a single physiologically based pharmacokinetic (PBPK) model that enables more confident extrapolation to humans. Because available data suggested there might be differences in PQ kinetics between primates and non-primates, a radiolabelled study was conducted to characterize pharmacokinetics and excretion in Cynomolgus monkeys. Following single intravenous doses of 0.01 or 0.1 mg paraquat dichloride/kg bw, plasma PQ concentration-time profiles were dose-proportional. Excretion up to 48 h (predominantly urinary) was 82.9%, with ca. 10% remaining unexcreted. In vitro blood binding was similar across Cynomolgus monkeys, humans and rat. Our PBPK model for the rat, mouse and dog, employing a single set of PQ-specific parameters, was scaled to Cynomolgus monkeys and well represented the measured plasma concentration-time profiles over 14 days. Addition of a cartilage compartment to the model better captured the percent remaining in the monkeys at 48 h, whilst having negligible effect on model predictions for the other species. The PBPK model performed well for all four species, demonstrating there is little difference in PQ kinetics between non-primates and primates enabling a more confident extrapolation to humans. Scaling of the PBPK model to humans, with addition of a human-specific dermal submodel based on in vitro human dermal absorption data, provides a valuable tool that could be employed in defining internal dosimetry to complement human health risk assessments.
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Affiliation(s)
- Alexander J Stevens
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Jerry L Campbell
- Ramboll Environment and Health Consulting, 3214 Charles B. Root Wynd Suite 130, Raleigh, NC 27612, USA.
| | - Kim Z Travis
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Harvey J Clewell
- Ramboll Environment and Health Consulting, 3214 Charles B. Root Wynd Suite 130, Raleigh, NC 27612, USA.
| | | | - Philip A Botham
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Andrew R Cook
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Daniel J Minnema
- Syngenta Crop Protection LLC, P.O. Box 18300, Greensboro, NC, USA.
| | - Douglas C Wolf
- Syngenta Crop Protection LLC, Research Triangle Park, NC 27709, USA.
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16
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Campbell JL, Travis KZ, Clewell HJ, Stevens AJ, Hinderliter PM, Andersen ME, Botham PA, Cook AR, Minnema DJ, Wolf DC. Integration of paraquat pharmacokinetic data across species using PBPK modelling. Toxicol Appl Pharmacol 2021; 417:115462. [PMID: 33631233 DOI: 10.1016/j.taap.2021.115462] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 02/12/2021] [Accepted: 02/14/2021] [Indexed: 11/15/2022]
Abstract
Paraquat dichloride (PQ) is a non-selective herbicide which has been the subject of numerous toxicology studies over more than 50 years. This paper describes the development of a physiologically-based pharmacokinetic (PBPK) model of PQ kinetics for the rat, mouse and dog, firstly to aid the interpretation of studies in which no kinetic measurements were made, and secondly to enable the future extension of the model to humans. Existing pharmacokinetic data were used to develop a model for the rat and mouse. Simulations with this preliminary model were then used to identify key data gaps and to design a new blood binding study to reduce uncertainty in critical aspects of the model. The new data provided evidence to support the model structure, and its predictive performance was then assessed against dog and rat datasets not used in model development. The PQ-specific model parameters are the same for all three species, with only the physiological parameters varying between species. This consistency across species provides a strong basis for extrapolation to other species, as demonstrated here for the dog. The model enables a wide range of PQ data to be linked together to provide a broad understanding of PQ pharmacokinetics in rodents and the dog, showing that the key aspects of PQ kinetics in these species are understood and adequately encapsulated within the model.
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Affiliation(s)
- Jerry L Campbell
- Ramboll Environment and Health Consulting, 3214 Charles B. Root Wynd Suite 130, Raleigh, NC 27612, USA.
| | - Kim Z Travis
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Harvey J Clewell
- Ramboll Environment and Health Consulting, 3214 Charles B. Root Wynd Suite 130, Raleigh, NC 27612, USA.
| | - Alexander J Stevens
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | | | - Melvin E Andersen
- Andersen ToxConsulting LLC, 424 Granite Lake CT, Denver, NC 28037, USA
| | - Philip A Botham
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Andrew R Cook
- Syngenta Ltd, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
| | - Daniel J Minnema
- Syngenta Crop Protection LLC, P.O. Box 18300, Greensboro, NC, USA.
| | - Douglas C Wolf
- Syngenta Crop Protection LLC, Research Triangle Park, NC 27709, USA.
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17
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Campbell JL, Otter R, Anderson WA, Longnecker MP, Clewell RA, North C, Clewell HJ. Development of a physiologically based pharmacokinetic model of diisononyl phthalate (DiNP) in pregnant rat and human. J Toxicol Environ Health A 2020; 83:631-648. [PMID: 32757748 DOI: 10.1080/15287394.2020.1798831] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A physiologically based pharmacokinetic (PBPK) model for di-isononyl phthalate (DiNP) was developed by adapting the existing models for di(2-ethylhexyl) phthalate (DEHP) and di-butylphthalate (DBP). Both pregnant rat and human time-course plasma and urine data were used to address the hydrolysis of DiNP in intestinal tract, plasma, and liver as well as hepatic oxidative metabolism and conjugation of the monoester and primary oxidative metabolites. Data in both rats and humans were available to inform the uptake and disposition of mono-isononyl phthalate (MiNP) as well as the three primary oxidative metabolites including hydroxy (7-OH)-, oxo (7-OXO)-, and carboxy (7-COX)-monoisononyl phthalate in plasma and urine. The DiNP model was reliable over a wide range of exposure levels in the pregnant rat as well as the two low exposure levels in humans including capturing the nonlinear behavior in the pregnant rat after repeated 750 mg/kg/day dosing. The presented DiNP PBPK model in pregnant rat and human, based upon an extensive kinetic dataset in both species, may provide a basis for assessing human equivalent exposures based upon either rodent or in vitro points of departure.
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Affiliation(s)
| | - Rainer Otter
- Regulatory Affairs/Advocacy, Basf Se , Ludwigshafen, Germany
| | - Warwick A Anderson
- Food Safety, Fera Science Ltd., National Agri-Food Innovation Campus , York, UK
| | | | | | - Colin North
- Toxicology & Environmental Science, ExxonMobil Biomedical Sciences, Inc , Annandale, NJ, USA
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18
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Clewell HJ, Campbell JL, Van Landingham C, Franzen A, Yoon M, Dodd DE, Andersen ME, Gentry PR. Response to "letter concerning: Clewell (2019) incorporation of in vitro metabolism data and physiologically based pharmacokinetic modeling in a risk assessment for chloroprene." (UIHT-2020-0053). Inhal Toxicol 2020; 32:369-371. [PMID: 32900235 DOI: 10.1080/08958378.2020.1817199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- H J Clewell
- Research Triangle Park, Ramboll US Corporation, Charlotte, North Carolina, USA
| | - J L Campbell
- Research Triangle Park, Ramboll US Corporation, Charlotte, North Carolina, USA
| | | | - A Franzen
- Ramboll US Corporation, Monroe, Louisiana, USA
| | - M Yoon
- ToxStrategies, Inc., Cary, North Carolina, USA
| | - D E Dodd
- Research Triangle Park, The Hamner Institutes for Health Sciences, North Carolina, USA
| | - M E Andersen
- Research Triangle Park, The Hamner Institutes for Health Sciences, North Carolina, USA
| | - P R Gentry
- ToxStrategies, Inc., Cary, North Carolina, USA
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19
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Price RJ, Scott MP, Cantrill C, Higgins LG, Moreau M, Yoon M, Clewell HJ, Creek MR, Osimitz TG, Houston JB, Lake BG. Kinetics of metabolism of deltamethrin and cis- and trans-permethrin in vitro. Studies using rat and human liver microsomes, isolated rat hepatocytes and rat liver cytosol. Xenobiotica 2020; 51:40-50. [PMID: 32757971 DOI: 10.1080/00498254.2020.1807075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The kinetics of metabolism of deltamethrin (DLM) and cis- and trans-permethrin (CPM and TPM) was studied in male Sprague-Dawley rat and human liver microsomes. DLM metabolism kinetics was also studied in isolated rat hepatocytes, liver microsomes and cytosol. Apparent intrinsic clearance (CLint) values for the metabolism of DLM, CPM and TPM by cytochrome P450 (CYP) and carboxylesterase (CES) enzymes in rat and human liver microsomes decreased with increasing microsomal protein concentration. However, when apparent CLint values were corrected for nonspecific binding to allow calculation of unbound (i.e., corrected) CLint values, the unbound values did not vary greatly with microsomal protein concentration. Unbound CLint values for metabolism of 0.05-1 μM DLM in rat liver microsomes (CYP and CES enzymes) and cytosol (CES enzymes) were not significantly different from rates of DLM metabolism in isolated rat hepatocytes. This study demonstrates that the nonspecific binding of these highly lipophilic compounds needs to be taken into account in order to obtain accurate estimates of rates of in vitro metabolism of these pyrethroids. While DLM is rapidly metabolised in vitro, the hepatocyte membrane does not appear to represent a barrier to the absorption and hence subsequent hepatic metabolism of this pyrethroid.
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Affiliation(s)
- Roger J Price
- Faculty of Health and Medical Sciences, University of Surrey, Surrey, UK
| | - Mary P Scott
- Faculty of Health and Medical Sciences, University of Surrey, Surrey, UK
| | - Carina Cantrill
- Centre for Applied Pharmacokinetic Research, University of Manchester, Manchester, UK
| | - Larry G Higgins
- Concept Life Sciences (formerly CXR Biosciences Ltd.), Dundee, UK
| | | | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, NC, USA
| | | | - Moire R Creek
- Moire Creek Toxicology Consulting Services, Lincoln, CA, USA
| | | | - J Brian Houston
- Centre for Applied Pharmacokinetic Research, University of Manchester, Manchester, UK
| | - Brian G Lake
- Faculty of Health and Medical Sciences, University of Surrey, Surrey, UK
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20
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Higgins LG, Chatham LR, Tomczynski SL, MacLeod AK, Moreau M, Clewell HJ, Yoon M, Creek MR, Osimitz TG, Lake BG. Differential lymphatic versus portal vein uptake of the synthetic pyrethroids deltamethrin and cis-permethrin in rats. Toxicology 2020; 443:152563. [PMID: 32805335 DOI: 10.1016/j.tox.2020.152563] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 07/14/2020] [Accepted: 08/10/2020] [Indexed: 10/23/2022]
Abstract
The objective of this study was to obtain data on pathways of absorption of the synthetic pyrethroids deltamethrin (DLM) and cis-permethrin (CPM) following oral administration to rats. Adult male Sprague-Dawley rats with cannulated mesenteric lymph ducts and hepatic portal veins were given single doses of either 5 mg/kg DLM or 60 mg/kg CPM via the duodenum and lymph and portal blood samples collected for up to 300 min. The pyrethroid dosing vehicles (5 mL/kg body weight) were either corn oil or glycerol formal. Levels of DLM and CPM in lymph and portal blood samples were determined by high-performance liquid chromatography-mass spectrometry-mass spectrometry. Over the time period studied, levels of both DLM and CPM following administration in either corn oil or glycerol formal were greater in lymph than in portal blood. Lymphatic uptake of both DLM and CPM was enhanced following dosing in glycerol formal than in corn oil. The results of this study suggest that after oral administration to rats, these two pyrethroids are predominantly absorbed via the lymphatic system rather than via portal blood. The data obtained in this study thus support a recently developed physiologically-based pharmacokinetic (PBPK) model to evaluate age-related differences in pyrethroid pharmacokinetics in the rat, where it was assumed that absorption of pyrethroids was predominantly via lymphatic uptake.
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Affiliation(s)
- Larry G Higgins
- Concept Life Sciences (Formerly CXR Biosciences Ltd.), 2, James Lindsay Place, Dundee Technopole, Dundee, DD1 5JJ, United Kingdom.
| | - Lynsey R Chatham
- Concept Life Sciences (Formerly CXR Biosciences Ltd.), 2, James Lindsay Place, Dundee Technopole, Dundee, DD1 5JJ, United Kingdom
| | - Sara L Tomczynski
- Concept Life Sciences (Formerly CXR Biosciences Ltd.), 2, James Lindsay Place, Dundee Technopole, Dundee, DD1 5JJ, United Kingdom
| | - A Kenneth MacLeod
- Concept Life Sciences (Formerly CXR Biosciences Ltd.), 2, James Lindsay Place, Dundee Technopole, Dundee, DD1 5JJ, United Kingdom
| | - Marjory Moreau
- ScitoVation, LLC, Research Triangle Park, NC, 27709, USA
| | | | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, NC, 27709, USA
| | - Moire R Creek
- Moire Creek Toxicology Consulting Services, Lincoln, CA, 95648, USA
| | | | - Brian G Lake
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, UK
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21
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Dzierlenga MW, Allen BC, Clewell HJ, Longnecker MP. Pharmacokinetic bias analysis of an association between clinical thyroid disease and two perfluoroalkyl substances. Environ Int 2020; 141:105784. [PMID: 32408218 DOI: 10.1016/j.envint.2020.105784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 04/06/2020] [Accepted: 04/30/2020] [Indexed: 06/11/2023]
Abstract
Exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) has been associated with the occurrence of thyroid disease in some epidemiologic studies. We hypothesized that in a specific epidemiologic study based on the National Health and Nutrition Examination Survey, the association of clinical thyroid disease with serum concentration of PFOA and PFOS was due to reverse causality. Thyroid hormone affects glomerular filtration, which in turn affects excretion of PFOA and PFOS. We evaluated this by linking a model of thyroid disease status over the lifetime to a physiologically based pharmacokinetic model of PFOA and PFOS. Using Monte Carlo methods, we simulated the target study population and analyzed the data using multivariable logistic regression. The target and simulated populations were similar with respect to age, estimated glomerular filtration rate, serum concentrations of PFOA and PFOS, and prevalence of clinical thyroid disease. The analysis showed little or no evidence of bias from the hypothesized mechanism. The largest bias was for the fourth quartile of PFOA in females, with an odds ratio of 0.93 (95% CI, 0.90, 0.97). The reported odds ratio of clinical thyroid disease for this group was 1.63 (1.07, 2.47), and if it were corrected for the bias would have been 1.74 (1.14, 2.65). Our results suggest that little of the reported association in the target study was due to reverse causality.
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22
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Mallick P, Song G, Efremenko AY, Pendse SN, Creek MR, Osimitz TG, Hines RN, Hinderliter P, Clewell HJ, Lake BG, Yoon M, Moreau M. Physiologically Based Pharmacokinetic Modeling in Risk Assessment: Case Study With Pyrethroids. Toxicol Sci 2020; 176:460-469. [PMID: 32421774 PMCID: PMC7416317 DOI: 10.1093/toxsci/kfaa070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
The assessment of potentially sensitive populations is an important application of risk assessment. To address the concern for age-related sensitivity to pyrethroid insecticides, life-stage physiologically based pharmacokinetic (PBPK) modeling supported by in vitro to in vivo extrapolation was conducted to predict age-dependent changes in target tissue exposure to 8 pyrethroids. The purpose of this age-dependent dosimetry was to calculate a Data-derived Extrapolation Factor (DDEF) to address age-related pharmacokinetic differences for pyrethroids in humans. We developed a generic human PBPK model for pyrethroids based on our previously published rat model that was developed with in vivo rat data. The results demonstrated that the age-related differences in internal exposure to pyrethroids in the brain are largely determined by the differences in metabolic capacity and in physiology for pyrethroids between children and adults. The most important conclusion from our research is that, given an identical external exposure, the internal (target tissue) concentration is equal or lower in children than in adults in response to the same level of exposure to a pyrethroid. Our results show that, based on the use of the life-stage PBPK models with 8 pyrethroids, DDEF values are essentially close to 1, resulting in a DDEF for age-related pharmacokinetic differences of 1. For risk assessment purposes, this indicates that no additional adjustment factor is necessary to account for age-related pharmacokinetic differences for these pyrethroids.
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Affiliation(s)
| | - Gina Song
- ScitoVation, LLC, Durham, North Carolina 27713
| | | | | | - Moire R Creek
- Moire Creek Toxicology Consulting Services, Lincoln, California 95648
| | | | - Ronald N Hines
- US EPA, Office of Research and Development, Center for Public Health and Environmental Assessment, Research Triangle Park, North Carolina 27709
| | | | | | - Brian G Lake
- Faculty of Health and Medical Sciences, University of Surrey, Surrey GU2 7XH, UK
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23
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Dzierlenga MW, Moreau M, Song G, Mallick P, Ward PL, Campbell JL, Housand C, Yoon M, Allen BC, Clewell HJ, Longnecker MP. Quantitative bias analysis of the association between subclinical thyroid disease and two perfluoroalkyl substances in a single study. Environ Res 2020; 182:109017. [PMID: 31865168 DOI: 10.1016/j.envres.2019.109017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Revised: 11/08/2019] [Accepted: 12/06/2019] [Indexed: 05/23/2023]
Abstract
Exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) has been associated with the occurrence of thyroid disease in some epidemiologic studies. We hypothesized that in a specific epidemiologic study based on the National Health and Nutrition Examination Survey, the association of subclinical thyroid disease with serum concentration of PFOA and PFOS was due to reverse causality. Thyroid hormone affects glomerular filtration, which in turn affects excretion of PFOA and PFOS. We evaluated this by linking a model of thyroid disease status over the lifetime to physiologically based pharmacokinetic models of PFOA and PFOS. Using Monte Carlo methods, we simulated the target study population and analyzed the data using multivariable logistic regression. The target and simulated populations were similar with respect to age, estimated glomerular filtration rate, serum concentrations of PFOA and PFOS, and prevalence of subclinical thyroid disease. Our findings suggest that in the target study the associations with subclinical hypothyroidism were overstated and the results for subclinical hyperthyroidism were, in general, understated. For example, for subclinical hypothyroidism in men, the reported odds ratio per ln(PFOS) increase was 1.98 (95% CI 1.19-3.28), whereas in the simulated data the bias due to reverse causality gave an odds ratio of 1.19 (1.16-1.23). Our results provide evidence of bias due to reverse causality in a specific cross-sectional study of subclinical thyroid disease with exposure to PFOA and PFOS among adults.
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Affiliation(s)
| | | | - Gina Song
- ScitoVation, LLC, Research Triangle Park, NC, USA
| | | | | | | | | | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, NC, USA; ToxStrategies, Research Triangle Park, NC, USA
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24
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Sax SN, Gentry PR, Van Landingham C, Clewell HJ, Mundt KA. Extended Analysis and Evidence Integration of Chloroprene as a Human Carcinogen. Risk Anal 2020; 40:294-318. [PMID: 31524302 PMCID: PMC7028114 DOI: 10.1111/risa.13397] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 05/09/2019] [Accepted: 08/09/2019] [Indexed: 05/11/2023]
Abstract
β-Chloroprene is used in the production of polychloroprene, a synthetic rubber. In 2010, Environmental Protection Agency (EPA) published the Integrated Risk Information System "Toxicological Review of Chloroprene," concluding that chloroprene was "likely to be carcinogenic to humans." This was based on findings from a 1998 National Toxicology Program (NTP) study showing multiple tumors within and across animal species; results from occupational epidemiological studies; a proposed mutagenic mode of action; and structural similarities with 1,3-butadiene and vinyl chloride. Using mouse data from the NTP study and assuming a mutagenic mode of action, EPA calculated an inhalation unit risk (IUR) for chloroprene of 5 × 10-4 per µg/m3 . This is among the highest IURs for chemicals classified by IARC or EPA as known or probable human carcinogens and orders of magnitude higher than the IURs for carcinogens such as vinyl chloride, benzene, and 1,3-butadiene. Due to differences in pharmacokinetics, mice appear to be uniquely responsive to chloroprene exposure compared to other animals, including humans, which is consistent with the lack of evidence of carcinogenicity in robust occupational epidemiological studies. We evaluated and integrated all lines of evidence for chloroprene carcinogenicity to assess whether the 2010 EPA IUR could be scientifically substantiated. Due to clear interspecies differences in carcinogenic response to chloroprene, we applied a physiologically based pharmacokinetic model for chloroprene to calculate a species-specific internal dose (amount metabolized/gram of lung tissue) and derived an IUR that is over 100-fold lower than the 2010 EPA IUR. Therefore, we recommend that EPA's IUR be updated.
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25
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Clewell HJ, Campbell JL, Van Landingham C, Franzen A, Yoon M, Dodd DE, Andersen ME, Gentry PR. Incorporation of in vitro metabolism data and physiologically based pharmacokinetic modeling in a risk assessment for chloroprene. Inhal Toxicol 2020; 31:468-483. [PMID: 31992090 DOI: 10.1080/08958378.2020.1715513] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Objective: To develop a physiologically based pharmacokinetic (PBPK) model for chloroprene in the mouse, rat and human, relying only on in vitro data to estimate tissue metabolism rates and partitioning, and to apply the model to calculate an inhalation unit risk (IUR) for chloroprene.Materials and methods: Female B6C3F1 mice were the most sensitive species/gender for lung tumors in the 2-year bioassay conducted with chloroprene. The PBPK model included tissue metabolism rate constants for chloroprene estimated from results of in vitro gas uptake studies using liver and lung microsomes. To assess the validity of the PBPK model, a 6-hr, nose-only chloroprene inhalation study was conducted with female B6C3F1 mice in which both chloroprene blood concentrations and ventilation rates were measured. The PBPK model was then used to predict dose measures - amounts of chloroprene metabolized in lungs per unit time - in mice and humans.Results: The mouse PBPK model accurately predicted in vivo pharmacokinetic data from the 6-hr, nose-only chloroprene inhalation study. The PBPK model was used to conduct a cancer risk assessment based on metabolism of chloroprene to reactive epoxides in the lung, the target tissue in mice. The IUR was over100-fold lower than the IUR from the EPA Integrated Risk Information System (IRIS), which was based on inhaled chloroprene concentration. The different result from the PBPK model risk assessment arises from use of the more relevant tissue dose metric, amount metabolized, rather than inhaled concentrationDiscussion and conclusions: The revised chloroprene PBPK model is based on the best available science, including new test animal in vivo validation, updated literature review and a Markov-Chain Monte Carlo analysis to assess parameter uncertainty. Relying on both mouse and human metabolism data also provides an important advancement in the use of quantitative in vitro to in vivo extrapolation (QIVIVE). Inclusion of the best available science is especially important when deriving a toxicity value based on species extrapolation for the potential carcinogenicity of a reactive metabolite.
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Affiliation(s)
| | | | | | | | | | - Darol E Dodd
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
| | - Melvin E Andersen
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
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26
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Yoon M, Ring C, Van Landingham CB, Suh M, Song G, Antonijevic T, Gentry PR, Taylor MD, Keene AM, Andersen ME, Clewell HJ. Assessing children's exposure to manganese in drinking water using a PBPK model. Toxicol Appl Pharmacol 2019; 380:114695. [PMID: 31394159 DOI: 10.1016/j.taap.2019.114695] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Revised: 07/20/2019] [Accepted: 07/30/2019] [Indexed: 12/27/2022]
Abstract
A previously published human PBPK model for manganese (Mn) in infants and children has been updated with Mn in drinking water as an additional exposure source. Built upon the ability to capture differences in Mn source-specific regulation of intestinal uptake in nursing infants who are breast-fed and formula-fed, the updated model now describes the bioavailability of Mn from drinking water in children of ages 0-18. The age-related features, including the recommended age-specific Mn dietary intake, age-specific water consumption rates, and age-specific homeostasis of Mn, are based on the available human data and knowledge of the biology of essential-metal homeostasis. Model simulations suggest that the impact of adding drinking-water exposure to daily Mn exposure via dietary intake and ambient air inhalation in children is not greater than the impacts in adults, even at a drinking-water concentration that is 2 times higher than the USEPA's lifetime health advisory value. This conclusion was also valid for formula-fed infants who are considered at the highest potential exposure to Mn from drinking water compared to all other age groups. Our multi-route, multi-source Mn PBPK model for infants and children provides insights about the potential for Mn-related health effects on growing children and will thereby improve the level of confidence in properly interpreting Mn exposure-health effects relationships in children in human epidemiological studies.
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Affiliation(s)
- M Yoon
- ToxStrategies, Inc., RTP, NC, USA.
| | - C Ring
- ToxStrategies, Inc., Austin, TX, USA
| | | | - M Suh
- ToxStrategies, Inc., Orange County, CA, USA
| | - G Song
- ToxStrategies, Inc., Orange County, CA, USA
| | | | | | | | - A M Keene
- Afton Chemical Corporation, Richmond, VA, USA
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Yoon M, Efremenko A, Van Landingham C, Gentry PR, Keene AM, Taylor MD, Clewell HJ, Andersen ME. Updating physiologically based pharmacokinetic models for manganese by incorporating rapid association/dissociation processes in tissues. Toxicol Appl Pharmacol 2019; 372:1-10. [PMID: 30978397 DOI: 10.1016/j.taap.2019.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 04/02/2019] [Accepted: 04/06/2019] [Indexed: 11/30/2022]
Abstract
Previously, we developed a series of physiologically based pharmacokinetic (PBPK) models for manganese (Mn) in which saturable tissue binding and dose-dependent increases in biliary excretion captured key aspects of Mn homeostasis biology. These models reproduced the non-linear behavior of Mn kinetics in different tissues, accounting for dose-dependent changes in Mn kinetics. The original model construct had relatively slow association and dissociation rate constants for Mn binding in tissues. In this updated model, both rates of entry into tissue and the interaction of Mn with binding sites are rapid, and the step limiting Mn accumulation is the saturation of tissue binding sites. This binding reflects general cellular requirements for Mn with high affinity but rapid exchange between bound and free forms, which we captured using a dissociation constant (KD) of ~ 0.5 μM across tissues while maintaining different maximum binding capacities in each tissue. Variability in the binding capacities accounted for different background levels of Mn in particular tissues. This alternative structure successfully described Mn kinetics in tissues in adult rats exposed to Mn either in their diet or by inhalation, indicating that both the original and the present models capture the dose-dependent and tissue-specific kinetic behavior of Mn in adult rats. Although the published models that emphasize the role of smaller tissue binding rate constants in non-linear behaviors capture all relevant dose-dependent kinetic behaviors of this metal, increasing biological relevance of the model structure and parameters should provide greater confidence in applying the Mn PBPK models to risk assessment.
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Affiliation(s)
- Miyoung Yoon
- ScitoVation, LLC, RTP, Cary, NC, USA; Toxstrategies, Inc., Cary, NC, USA.
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Andersen ME, Gentry PR, Swenberg JA, Mundt KA, White KW, Thompson C, Bus J, Sherman JH, Greim H, Bolt H, Marsh GM, Checkoway H, Coggon D, Clewell HJ. Considerations for refining the risk assessment process for formaldehyde: Results from an interdisciplinary workshop. Regul Toxicol Pharmacol 2019; 106:210-223. [PMID: 31059732 DOI: 10.1016/j.yrtph.2019.04.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 04/17/2019] [Accepted: 04/21/2019] [Indexed: 01/06/2023]
Abstract
Anticipating the need to evaluate and integrate scientific evidence to inform new risk assessments or to update existing risk assessments, the Formaldehyde Panel of the American Chemistry Council (ACC), in collaboration with the University of North Carolina, convened a workshop: "Understanding Potential Human Health Cancer Risk - From Data Integration to Risk Evaluation" in October 2017. Twenty-four (24) invited-experts participated with expertise in epidemiology, toxicology, science integration and risk evaluation. Including members of the organizing committee, there were 29 participants. The meeting included eleven presentations encompassing an introduction and three sessions: (1) "integrating the formaldehyde science on nasal/nasopharyngeal carcinogenicity and potential for causality"; (2) "integrating the formaldehyde science on lymphohematopoietic cancer and potential for causality; and, (3) "formaldehyde research-data suitable for risk assessment". Here we describe key points from the presentations on epidemiology, toxicology and mechanistic studies that should inform decisions about the potential carcinogenicity of formaldehyde in humans and the discussions about approaches for structuring an integrated, comprehensive risk assessment for formaldehyde. We also note challenges expected when attempting to reconcile divergent results observed from research conducted within and across different scientific disciplines - especially toxicology and epidemiology - and in integrating diverse, multi-disciplinary mechanistic evidence.
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Affiliation(s)
- Melvin E Andersen
- ScitoVation LLC, 100 Capitola Drive, Drive 106, Durham, NC, 27713, USA.
| | | | - James A Swenberg
- Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, NC, USA
| | - Kenneth A Mundt
- Ramboll US Corporation, Amherst, MA (currently with Cardno Chemrisk, Boston, MA, USA
| | | | | | - James Bus
- Center for Toxicology and Mechanistic Biology, Exponent, Alexandria, VA, USA
| | | | | | - Hermann Bolt
- Leibniz Institute for Working Environment and Human Factors (IfADo), Dortmund, Germany
| | - Gary M Marsh
- Department of Biostatistics, Center for Occupational Biostatistics and Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA
| | - Harvey Checkoway
- University of California, San Diego, Department of Family Medicine and Public Health, USA
| | - David Coggon
- MRC Lifecourse Epidemiology Unit, University of Southampton, United Kingdom
| | - Harvey J Clewell
- Ramboll US Corporation, 6 Davis Drive, Suite 13, Research Triangle Park, NC, 27709, USA
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Dzierlenga MW, Yoon M, Wania F, Ward PL, Armitage JM, Wood SA, Clewell HJ, Longnecker MP. Quantitative bias analysis of the association of type 2 diabetes mellitus with 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153). Environ Int 2019; 125:291-299. [PMID: 30735960 DOI: 10.1016/j.envint.2018.12.036] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 12/14/2018] [Accepted: 12/17/2018] [Indexed: 06/09/2023]
Abstract
An association between serum concentrations of persistent organic pollutants (POPs), such as 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153), and risk of type 2 diabetes mellitus (T2DM) has been reported. Conditional on body mass index (BMI) and waist circumference (WC), a higher serum PCB-153 concentration may be a marker of T2DM risk because it reflects other aspects of obesity that are related to T2DM risk and to PCB-153 clearance. To estimate the amount of residual confounding by other aspects of obesity, we performed a quantitative bias analysis on the results of a specific study. A physiologically-based pharmacokinetic (PBPK) model was developed to predict serum levels of PCB-153 for a simulated population. T2DM status was assigned to simulated subjects based on age, sex, BMI, WC, and visceral adipose tissue mass. The distributions of age, BMI, WC, and T2DM prevalence of the simulated population were tailored to closely match the target population. Analysis of the simulated data showed that a small part of the observed association appeared to be due to residual confounding. For example, the predicted odds ratio of T2DM that would have been obtained had the results been adjusted for visceral adipose tissue mass, for the ≥90th percentile of PCB-153 serum concentration, was 6.60 (95% CI 2.46-17.74), compared with an observed odds ratio of 7.13 (95% CI 2.65-19.13). Our results predict that the association between PCB-153 and risk of type 2 diabetes mellitus would not be substantially changed by additional adjustment for visceral adipose tissue mass in epidemiologic analyses. Confirmation of these predictions with longitudinal data would be reassuring.
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Affiliation(s)
| | - M Yoon
- ScitoVation, LLC, Research Triangle Park, NC, USA
| | - F Wania
- University of Toronto Scarborough, Toronto, Ontario, Canada
| | - P L Ward
- Ramboll, Research Triangle Park, NC, USA
| | - J M Armitage
- University of Toronto Scarborough, Toronto, Ontario, Canada
| | - S A Wood
- University of Toronto Scarborough, Toronto, Ontario, Canada
| | - H J Clewell
- ScitoVation, LLC, Research Triangle Park, NC, USA
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Tsuji JS, Chang ET, Gentry PR, Clewell HJ, Boffetta P, Cohen SM. Dose-response for assessing the cancer risk of inorganic arsenic in drinking water: the scientific basis for use of a threshold approach. Crit Rev Toxicol 2019; 49:36-84. [DOI: 10.1080/10408444.2019.1573804] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
| | - Ellen T. Chang
- Exponent, Inc., Menlo Park, CA and Stanford Cancer Institute, Stanford, CA, USA
| | | | | | - Paolo Boffetta
- Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Samuel M. Cohen
- Havlik-Wall Professor of Oncology, Department of Pathology and Microbiology and the Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE, USA
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Ellison CA, Blackburn KL, Carmichael PL, Clewell HJ, Cronin MTD, Desprez B, Escher SE, Ferguson SS, Grégoire S, Hewitt NJ, Hollnagel HM, Klaric M, Patel A, Salhi S, Schepky A, Schmitt BG, Wambaugh JF, Worth A. Challenges in working towards an internal threshold of toxicological concern (iTTC) for use in the safety assessment of cosmetics: Discussions from the Cosmetics Europe iTTC Working Group workshop. Regul Toxicol Pharmacol 2019; 103:63-72. [PMID: 30653989 PMCID: PMC6644721 DOI: 10.1016/j.yrtph.2019.01.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Revised: 01/02/2019] [Accepted: 01/07/2019] [Indexed: 11/22/2022]
Abstract
The Threshold of Toxicological Concern (TTC) is an important risk assessment tool which establishes acceptable low-level exposure values to be applied to chemicals with limited toxicological data. One of the logical next steps in the continued evolution of TTC is to develop this concept further so that it is representative of internal exposures (TTC based on plasma concentration). An internal TTC (iTTC) would provide threshold values that could be utilized in exposure-based safety assessments. As part of a Cosmetics Europe (CosEu) research program, CosEu has initiated a project that is working towards the development of iTTCs that can be used for the human safety assessment. Knowing that the development of an iTTC is an ambitious and broad-spanning topic, CosEu organized a Working Group comprised a balance of multiple stakeholders (cosmetics and chemical industries, the EPA and JRC and academia) with relevant experience and expertise and workshop to critically evaluate the requirements to establish an iTTC. Outcomes from the workshop included an evaluation on the current state of the science for iTTC, the overall iTTC strategy, selection of chemical databases, capture and curation of chemical information, ADME and repeat dose data, expected challenges, as well as next steps and ongoing work.
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Affiliation(s)
- Corie A Ellison
- The Procter & Gamble Company, Cincinnati, OH, United States.
| | | | - Paul L Carmichael
- Unilever Safety and Environmental Assurance Center, Bedfordshire, UK
| | | | - Mark T D Cronin
- School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool, England, UK
| | | | - Sylvia E Escher
- Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover, Germany
| | - Steve S Ferguson
- National Institute of Environmental Health Sciences, North Carolina, United States
| | | | | | | | | | - Atish Patel
- Research Institute for Fragrance Materials, New Jersey, United States
| | | | | | | | - John F Wambaugh
- United States Environmental Protection Agency, National Center for Computational Toxicology, North Carolina, United States
| | - Andrew Worth
- European Commission, Joint Research Centre, Ispra, Italy
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Song G, Moreau M, Efremenko A, Lake BG, Wu H, Bruckner JV, White CA, Osimitz TG, Creek MR, Hinderliter PM, Clewell HJ, Yoon M. Evaluation of Age-Related Pyrethroid Pharmacokinetic Differences in Rats: Physiologically-Based Pharmacokinetic Model Development Using In Vitro Data and In Vitro to In Vivo Extrapolation. Toxicol Sci 2019; 169:365-379. [DOI: 10.1093/toxsci/kfz042] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Affiliation(s)
- Gina Song
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
| | - Marjory Moreau
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
| | - Alina Efremenko
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
| | - Brian G Lake
- Centre for Toxicology, University of Surrey, Surrey, UK
| | - Huali Wu
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
- Duke Medical Center, Durham, North Carolina 27705
| | | | | | | | - Moire R Creek
- Valent USA, LLC, Walnut Creek, California 94596
- Moire Creek Toxicology Consulting Services, Livermore, California 94550
| | | | - Harvey J Clewell
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
- Ramboll, Research Triangle Park, North Carolina 27709
| | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, North Carolina, 27709
- ToxStrategies, Cary, North Carolina 27511
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Travis KZ, Clewell HJ, Campbell JL, Hinderliter PM. Letter to the editor re: Cheng, YH., Chou, WC., Yang, YF. et al. Environ Sci Pollut Res (2017). https://doi.org/10.1007/s11356-017-0875-4. Environ Sci Pollut Res Int 2018; 25:33832-33835. [PMID: 30291613 PMCID: PMC6245011 DOI: 10.1007/s11356-018-3371-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 09/28/2018] [Indexed: 06/08/2023]
Affiliation(s)
- Kim Z Travis
- Syngenta Ltd, Jealott’s Hill International Research Centre, Bracknell, Berkshire RG42 6EY UK
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Clewell HJ, Yager JW, Greene TB, Gentry PR. Application of the adverse outcome pathway (AOP) approach to inform mode of action (MOA): A case study with inorganic arsenic. J Toxicol Environ Health A 2018; 81:893-912. [PMID: 30230972 DOI: 10.1080/15287394.2018.1500326] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 07/10/2018] [Accepted: 07/10/2018] [Indexed: 06/08/2023]
Abstract
The aim of this study was to establish a process for deriving a chemical-specific mode of action (MOA) from chemical-agnostic adverse outcome pathway (AOPs), using inorganic arsenic (iAs) as a case study. The AOP developed for this case study are related to disruption of cellular signaling by chemicals that strongly bind to vicinal dithiols in cellular proteins, leading to disruption of inflammatory and oxidative stress signaling along with inhibition of the DNA damage responses. The proposed MOA for iAs incorporates this AOP, overlaid on a background of increasing oxidative stress and/or co-exposure to mutagenic chemicals or radiation. The most challenging aspect of developing a MOA from AOP is the incorporation of metabolism and dose-response, neither of which may be considered in the development of an AOP. The cellular responses to relatively low concentrations (below 100 parts per billion) of iAs in drinking water appear to be secondary to binding of trivalent arsenite and its trivalent metabolite, monomethyl arsenous acid to key cellular vicinal dithiols in target tissues, resulting in a co-carcinogenic MOA. The proposed AOP may also be applied to non-cancer endpoints, enabling an integrated approach to conducting a risk assessment for iAs.
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Wetmore BA, Clewell RA, Cholewa B, Parks B, Pendse SN, Black MB, Mansouri K, Haider S, Berg EL, Judson RS, Houck KA, Martin M, Clewell HJ, Andersen ME, Thomas RS, McMullen PD. Assessing bioactivity-exposure profiles of fruit and vegetable extracts in the BioMAP profiling system. Toxicol In Vitro 2018; 54:41-57. [PMID: 30218698 DOI: 10.1016/j.tiv.2018.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 08/24/2018] [Accepted: 09/10/2018] [Indexed: 12/20/2022]
Abstract
The ToxCast program has generated in vitro screening data on over a thousand chemicals to assess potential disruption of important biological processes and assist in hazard identification and chemical testing prioritization. Few results have been reported for complex mixtures. To extend these ToxCast efforts to mixtures, we tested extracts from 30 organically grown fruits and vegetables in concentration-response in the BioMAP® assays. BioMAP systems use human primary cells primed with endogenous pathway activators to identify phenotypic perturbations related to proliferation, inflammation, immunomodulation, and tissue remodeling. Clustering of bioactivity profiles revealed separation of these produce extracts and ToxCast chemicals. Produce extracts elicited 87 assay endpoint responses per item compared to 20 per item for ToxCast chemicals. On a molar basis, the produce extracts were 10 to 50-fold less potent and when constrained to the maximum testing concentration of the ToxCast chemicals, the produce extracts did not show activity in as many assay endpoints. Using intake adjusted measures of dose, the bioactivity potential was higher for produce extracts than for agrichemicals, as expected based on the comparatively small amounts of agrichemical residues present on conventionally grown produce. The evaluation of BioMAP readouts and the dose responses for produce extracts showed qualitative and quantitative differences from results with single chemicals, highlighting challenges in the interpretation of bioactivity data and dose-response from complex mixtures.
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Affiliation(s)
- Barbara A Wetmore
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States; United States Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, Research Triangle Park, NC, United States
| | - Rebecca A Clewell
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Brian Cholewa
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Bethany Parks
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Salil N Pendse
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Michael B Black
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Kamel Mansouri
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Saad Haider
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Ellen L Berg
- Eurofins DiscoverX, Burlingame, CA, United States
| | - Richard S Judson
- United States Environmental Protection Agency, Office of Research and Development, National Center for Computational Toxicology, Research Triangle Park, NC, United States
| | - Keith A Houck
- United States Environmental Protection Agency, Office of Research and Development, National Center for Computational Toxicology, Research Triangle Park, NC, United States
| | - Matthew Martin
- United States Environmental Protection Agency, Office of Research and Development, National Center for Computational Toxicology, Research Triangle Park, NC, United States
| | - Harvey J Clewell
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Melvin E Andersen
- ScitoVation, 6 Davis Drive, Research Triangle Park, NC, United States
| | - Russell S Thomas
- United States Environmental Protection Agency, Office of Research and Development, National Center for Computational Toxicology, Research Triangle Park, NC, United States
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Phillips MB, Balbuena-Venancio P, Enders JR, Norini RL, Shim YS, Burgunder E, Rao L, Billings D, Pedersen J, Macdonald JM, Andersen M, Clewell HJ, Yoon M. Xenobiotic Metabolism in Alginate-Encapsulated Primary Human Hepatocytes Over Long Timeframes. ACTA ACUST UNITED AC 2018. [DOI: 10.1089/aivt.2017.0029] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
| | - Pergentino Balbuena-Venancio
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | | | | | - Yoo-Sik Shim
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | - Erin Burgunder
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | - Lavanya Rao
- ScitoVation, LLC, Research Triangle Park, North Carolina
| | - David Billings
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | - Jenny Pedersen
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | - Jeffrey M. Macdonald
- Joint Department of Biomedical Engineering, University of North Carolina, Chapel Hill, North Carolina
| | - Melvin Andersen
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | - Harvey J. Clewell
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
| | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, North Carolina
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina
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Campbell JL, Yoon M, Ward PL, Fromme H, Kessler W, Phillips MB, Anderson WA, Clewell HJ, Longnecker MP. Excretion of Di-2-ethylhexyl phthalate (DEHP) metabolites in urine is related to body mass index because of higher energy intake in the overweight and obese. Environ Int 2018; 113:91-99. [PMID: 29421411 DOI: 10.1016/j.envint.2018.01.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 01/12/2018] [Accepted: 01/22/2018] [Indexed: 05/20/2023]
Abstract
A higher body mass index (BMI) has been positively associated with the rate of excretion of di-2-ethylhexyl phthalate (DEHP) metabolites in urine in data from the National Health and Nutrition Examination Survey (NHANES), suggesting an association between DEHP exposure and BMI. The association, however, may be due to the association between body mass maintenance and higher energy intake, with higher energy intake being accompanied by a higher intake of DEHP. To examine this hypothesis, we ran a Monte Carlo simulation with a DEHP physiologically-based pharmacokinetic (PBPK) model for adult humans. A realistic exposure sub-model was used, which included the relation of body weight to energy intake and of energy intake to DEHP intake. The model simulation output, when compared with urinary metabolite data from NHANES, supported good model validity. The distribution of BMI in the simulated population closely resembled that in the NHANES population. This indicated that the simulated subjects and DEHP exposure model were closely aligned with the NHANES population of interest. In the simulated population, the ordinary least squares regression coefficient for log(BMI) as a function of log(DEHP nmol/min) was 0.048 (SE 0.001), as compared with the reported value of 0.019 (SE 0.005). In other words, given our model structure, the higher energy intake in the overweight and obese, and the concomitant higher DEHP exposure, describes the reported relationship between BMI and DEHP.
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Affiliation(s)
| | - Miyoung Yoon
- ScitoVation, LLC, Research Triangle Park, NC 27709, USA
| | - Peyton L Ward
- Ramboll Environ, Research Triangle Park, NC 27709, USA
| | - Hermann Fromme
- Bavarian Health and Food Safety Authority, Munich, Germany
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Strope CL, Mansouri K, Clewell HJ, Rabinowitz JR, Stevens C, Wambaugh JF. High-throughput in-silico prediction of ionization equilibria for pharmacokinetic modeling. Sci Total Environ 2018; 615:150-160. [PMID: 28964990 PMCID: PMC6055917 DOI: 10.1016/j.scitotenv.2017.09.033] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 08/30/2017] [Accepted: 09/04/2017] [Indexed: 05/16/2023]
Abstract
Chemical ionization plays an important role in many aspects of pharmacokinetic (PK) processes such as protein binding, tissue partitioning, and apparent volume of distribution at steady state (Vdss). Here, estimates of ionization equilibrium constants (i.e., pKa) were analyzed for 8132 pharmaceuticals and 24,281 other compounds to which humans might be exposed in the environment. Results revealed broad differences in the ionization of pharmaceutical chemicals and chemicals with either near-field (in the home) or far-field sources. The utility of these high-throughput ionization predictions was evaluated via a case-study of predicted PK Vdss for 22 compounds monitored in the blood and serum of the U.S. population by the U.S. Centers for Disease Control and Prevention National Health and Nutrition Examination Survey (NHANES). The chemical distribution ratio between water and tissue was estimated using predicted ionization states characterized by pKa. Probability distributions corresponding to ionizable atom types (IATs) were then used to analyze the sensitivity of predicted Vdss on predicted pKa using Monte Carlo methods. 8 of the 22 compounds were predicted to be ionizable. For 5 of the 8 the predictions based upon ionization are significantly different from what would be predicted for a neutral compound. For all but one (foramsulfuron), the probability distribution of predicted Vdss generated by IAT sensitivity analysis spans both the neutral prediction and the prediction using ionization. As new data sets of chemical-specific information on metabolism and excretion for hundreds of chemicals are being made available (e.g., Wetmore et al., 2015), high-throughput methods for calculating Vdss and tissue-specific PK distribution coefficients will allow the rapid construction of PK models to provide context for both biomonitoring data and high-throughput toxicity screening studies such as Tox21 and ToxCast.
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Affiliation(s)
- Cory L Strope
- Risk Assessment Division, Office of Pollution Prevention and Toxics, Office of Chemical Safety and Pollution Prevention, U.S. Environmental Protection Agency, Washington, DC, USA; ORISE Postdoctoral Research Fellow, National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA; The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA.
| | - Kamel Mansouri
- ORISE Postdoctoral Research Fellow, National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA; ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC, USA
| | - Harvey J Clewell
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC, USA
| | - James R Rabinowitz
- National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA
| | - Caroline Stevens
- Ecosystems Research Division, National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA, USA
| | - John F Wambaugh
- National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC, USA
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McMullen PD, Andersen ME, Cholewa B, Clewell HJ, Dunnick KM, Hartman JK, Mansouri K, Minto MS, Nicolas CI, Phillips MB, Slattery S, Yoon M, Clewell RA. Evaluating opportunities for advancing the use of alternative methods in risk assessment through the development of fit-for-purpose in vitro assays. Toxicol In Vitro 2018; 48:310-317. [PMID: 29391263 DOI: 10.1016/j.tiv.2018.01.027] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 12/27/2017] [Accepted: 01/29/2018] [Indexed: 12/11/2022]
Abstract
An evolving regulatory, scientific, and legislative landscape is driving a fundamental change in how chemical safety decisions are made. As we move to implement changes, regulatory agencies and industry are beginning to adopt tiered approaches, which leverage high-throughput screening technologies for prioritization and read across, followed by interrogation of "hit chemicals" with more rigorous dose-response assessment either in fit-for-purpose human cell-based assays or with traditional in vivo tests. However, to date, suitable in vitro alternatives do not exist for the vast majority of the organ toxicities that form the basis of current regulatory decisions. To successfully support safety decisions, biologically relevant, quantitative, cell-based assays that evaluate dose-response and identify regions of safety for chemical exposure are required. This review evaluates the current state of the science in the development of such assays, identifies key gaps in the current tests, and recommends areas where research efforts may be focused to help move the risk assessment community towards more wide-spread use of in vitro methods. Our analysis suggests that a key shortcoming in the current efforts is the ability to test volatile compounds and to predict pulmonary toxicity. We present a mechanistically-based path forward for the development of a fit-for-purpose lung toxicity assay.
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Affiliation(s)
| | | | - Brian Cholewa
- ScitoVation, LLC., Research Triangle Park, NC 27709, United States
| | - Harvey J Clewell
- ScitoVation, LLC., Research Triangle Park, NC 27709, United States
| | | | | | - Kamel Mansouri
- ScitoVation, LLC., Research Triangle Park, NC 27709, United States
| | - Melyssa S Minto
- ScitoVation, LLC., Research Triangle Park, NC 27709, United States
| | | | | | - Scott Slattery
- ScitoVation, LLC., Research Triangle Park, NC 27709, United States
| | - Miyoung Yoon
- ScitoVation, LLC., Research Triangle Park, NC 27709, United States
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Yoon M, Phillips MB, Enders JR, Balbuena-Venancio P, Billings D, Norini R, Karsten R, Clewell HJ. Alginate-encapsulated primary human hepatocyte culture system to increase the accuracy of the predicted in vivo half-life of low clearance compounds. Drug Metab Pharmacokinet 2018. [DOI: 10.1016/j.dmpk.2017.11.232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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van Eijkeren JC, de Vries I, Bradberry SM, Vale JA, Clewell HJ, Hunault CC. Validation of a model predicting the effect of 2,3-dimercaptosuccinic acid (DMSA) chelation therapy in patients intoxicated by lead. Toxicol Lett 2017. [DOI: 10.1016/j.toxlet.2017.07.786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Ngueta G, Longnecker MP, Yoon M, Ruark CD, Clewell HJ, Andersen ME, Verner MA. Quantitative bias analysis of a reported association between perfluoroalkyl substances (PFAS) and endometriosis: The influence of oral contraceptive use. Environ Int 2017; 104:118-121. [PMID: 28392065 DOI: 10.1016/j.envint.2017.03.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 03/27/2017] [Accepted: 03/28/2017] [Indexed: 05/20/2023]
Abstract
An association between serum levels of perfluoroalkyl substances (PFAS) and endometriosis has recently been reported in an epidemiologic study. Oral contraceptive use to treat dysmenorrhea (pelvic pain associated with endometriosis) could potentially influence this association by reducing menstrual fluid loss, a route of excretion for PFAS. In this study, we aimed to evaluate the influence of differential oral contraceptive use on the association between PFAS and endometriosis. We used a published life-stage physiologically based pharmacokinetic (PBPK) model to simulate plasma levels of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from birth to age at study participation (range 18-44years). In the simulated population, PFAS level distributions matched those for controls in the epidemiologic study. Prevalence and geometric mean duration (standard deviation [SD]) of oral contraceptive use in the simulated women were based on data from the National Health and Nutrition Examination Survey; among the women with endometriosis the values were, respectively, 29% and 6.8 (3.1) years; among those without endometriosis these values were 18% and 5.3 (2.8) years. In simulations, menstrual fluid loss (ml/cycle) in women taking oral contraceptives was assumed to be 56% of loss in non-users. We evaluated the association between simulated plasma PFAS concentration and endometriosis in the simulated population using logistic regression. Based on the simulations, the association between PFAS levels and endometriosis attributable to differential contraceptive use had an odds ratio (95% CI) of 1.05 (1.02, 1.07) for a loge unit increase in PFOA and 1.03 (1.02, 1.05) for PFOS. In comparison, the epidemiologic study reported odds ratios of 1.62 (0.99, 2.66) for PFOA and 1.25 (0.87, 1.80) for PFOS. Our results suggest that the influence of oral contraceptive use on the association between PFAS levels and endometriosis is relatively small.
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Affiliation(s)
- Gerard Ngueta
- Department of Occupational and Environmental Health, Université de Montréal, 2375 chemin de la Cote-Sainte-Catherine, Montreal, QC H3T 1A8, Canada; Universite de Montreal Public Health Research Institute (IRSPUM), Université de Montréal, 7101, Parc Ave., Montreal, QC H3N 1X7, Canada.
| | | | - Miyoung Yoon
- ScitoVation, 6 Davis Dr, Research Triangle Park, NC 27709, USA.
| | | | - Harvey J Clewell
- Ramboll Environ, 6 Davis Dr, Research Triangle Park, NC 27709, USA; ScitoVation, 6 Davis Dr, Research Triangle Park, NC 27709, USA.
| | - Melvin E Andersen
- Ramboll Environ, 6 Davis Dr, Research Triangle Park, NC 27709, USA; ScitoVation, 6 Davis Dr, Research Triangle Park, NC 27709, USA.
| | - Marc-André Verner
- Department of Occupational and Environmental Health, Université de Montréal, 2375 chemin de la Cote-Sainte-Catherine, Montreal, QC H3T 1A8, Canada; Universite de Montreal Public Health Research Institute (IRSPUM), Université de Montréal, 7101, Parc Ave., Montreal, QC H3N 1X7, Canada.
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Campbell JL, Andersen ME, Van Landingham C, Gentry R, Jensen E, Domoradzki JY, Clewell HJ. Refinement of the oral exposure description in the cyclic siloxane PBPK model for rats and humans: Implications for exposure assessment. Toxicol Lett 2017; 279 Suppl 1:125-135. [PMID: 28408153 DOI: 10.1016/j.toxlet.2017.04.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 04/05/2017] [Accepted: 04/06/2017] [Indexed: 11/25/2022]
Abstract
The multi-compound, and multi-dose (MC-MD) route physiologically based pharmacokinetic (PBPK) model for cyclic siloxanes reported by McMullin et al. (2016) brought together the series of models for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) in rat and human into a unified code structure that would allow simulation of both compounds following the inhalation and dermal routes of exposure. The refined MC-MD PBPK model presented here expands upon this effort to include representation of rat kinetic data in plasma, tissues and exhaled breath for the parent compounds after oral bolus administration. Additional refinements were made with regards to hepatic induction of metabolism in the liver and allometric scaling of rate constants for the deep tissue compartments which will allow the MC-MD model to be used in uncertainty analysis. Overall, the refined MC-MD model was able to reproduce both parent D4 and D5 kinetic data in rat and human after inhalation exposure (rat and human) or dermal exposure (human). The inclusion of sequestered (i.e., lipid associated) oral absorption into plasma after oral bolus dosing successfully described the lack of exhalation as well as the initial distribution of siloxane to the liver which was higher than simple partitioning from plasma would allow. The refined MC-MD PBPK model presented here can be incorporated into uncertainty and variability analysis and cross-species dosimetry for both D4 and D5.
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Affiliation(s)
- Jerry L Campbell
- Ramboll Environ, 6 Davis Drive, Research Triangle Park, NC 27709, United States.
| | - Melvin E Andersen
- ScitoVation, LLC, 6 Davis Drive, Research Triangle Park, NC 27709, United States
| | | | - Robinan Gentry
- Ramboll Environ, 3107 Armand St., Monroe, LA 71201, United States
| | - Elke Jensen
- Dow Corning Corporation, 2200 W. Salzburg Road, Midland, MI 48686, United States
| | - Jean Y Domoradzki
- Dow Corning Corporation, 2200 W. Salzburg Road, Midland, MI 48686, United States
| | - Harvey J Clewell
- ScitoVation, LLC, 6 Davis Drive, Research Triangle Park, NC 27709, United States
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Gentry PR, Van Landingham C, Fuller WG, Sulsky SI, Greene TB, Clewell HJ, Andersen ME, Roels HA, Taylor MD, Keene AM. A tissue dose-based comparative exposure assessment of manganese using physiologically based pharmacokinetic modeling-The importance of homeostatic control for an essential metal. Toxicol Appl Pharmacol 2017; 322:27-40. [PMID: 28237878 DOI: 10.1016/j.taap.2017.02.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 02/17/2017] [Accepted: 02/20/2017] [Indexed: 01/27/2023]
Abstract
A physiologically-based pharmacokinetic (PBPK) model (Schroeter et al., 2011) was applied to simulate target tissue manganese (Mn) concentrations following occupational and environmental exposures. These estimates of target tissue Mn concentrations were compared to determine margins of safety (MOS) and to evaluate the biological relevance of applying safety factors to derive acceptable Mn air concentrations. Mn blood concentrations measured in occupational studies permitted verification of the human PBPK models, increasing confidence in the resulting estimates. Mn exposure was determined based on measured ambient air Mn concentrations and dietary data in Canada and the United States (US). Incorporating dietary and inhalation exposures into the models indicated that increases in target tissue concentrations above endogenous levels only begin to occur when humans are exposed to levels of Mn in ambient air (i.e. >10μg/m3) that are far higher than those currently measured in Canada or the US. A MOS greater than three orders of magnitude was observed, indicating that current Mn air concentrations are far below concentrations that would be required to produce the target tissue Mn concentrations associated with subclinical neurological effects. This application of PBPK modeling for an essential element clearly demonstrates that the conventional application of default factors to "convert" an occupational exposure to an equivalent continuous environmental exposure, followed by the application of safety factors, is not appropriate in the case of Mn. PBPK modeling demonstrates that the relationship between ambient Mn exposures and dose-to-target tissue is not linear due to normal tissue background levels and homeostatic controls.
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Affiliation(s)
- P Robinan Gentry
- Ramboll Environ US Corporation, 3701 Armand St., Monroe, LA 71201, United States.
| | | | - William G Fuller
- Ramboll Environ US Corporation, 3701 Armand St., Monroe, LA 71201, United States
| | | | - Tracy B Greene
- Ramboll Environ US Corporation, 3701 Armand St., Monroe, LA 71201, United States
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Song G, Sun X, Hines RN, McCarver DG, Lake BG, Osimitz TG, Creek MR, Clewell HJ, Yoon M. Determination of Human Hepatic CYP2C8 and CYP1A2 Age-Dependent Expression to Support Human Health Risk Assessment for Early Ages. Drug Metab Dispos 2017; 45:468-475. [PMID: 28228413 DOI: 10.1124/dmd.116.074583] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Accepted: 02/13/2017] [Indexed: 11/22/2022] Open
Abstract
Predicting age-specific metabolism is important for evaluating age-related drug and chemical sensitivity. Multiple cytochrome P450s and carboxylesterase enzymes are responsible for human pyrethroid metabolism. Complete ontogeny data for each enzyme are needed to support in vitro to in vivo extrapolation (IVIVE). This study was designed to determine age-dependent human hepatic CYP2C8 expression, for which only limited ontogeny data are available, and to further define CYP1A2 ontogeny. CYP2C8 and 1A2 protein levels were measured by quantitative Western blotting using liver microsomal samples prepared from 222 subjects with ages ranging from 8 weeks gestation to 18 years after birth. The median CYP2C8 expression was significantly greater among samples from subjects older than 35 postnatal days (n = 122) compared with fetal samples and those from very young infants (fetal to 35 days postnatal, n = 100) (0.00 vs. 13.38 pmol/mg microsomal protein; p < 0.0001). In contrast, the median CYP1A2 expression was significantly greater after 15 months postnatal age (n = 55) than in fetal and younger postnatal samples (fetal to 15 months postnatal, n = 167) (0.0167 vs. 2.354 pmol/mg microsomal protein; p < 0.0001). CYP2C8, but not CYP1A2, protein levels significantly correlated with those of CYP2C9, CYP2C19, and CYP3A4 (p < 0.001), consistent with CYP2C8 and CYP1A2 ontogeny probably being controlled by different mechanisms. This study provides key data for the physiologically based pharmacokinetic model-based prediction of age-dependent pyrethroid metabolism, which will be used for IVIVE to support pyrethroid risk assessment for early life stages.
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Affiliation(s)
- Gina Song
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Xueying Sun
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Ronald N Hines
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - D Gail McCarver
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Brian G Lake
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Thomas G Osimitz
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Moire R Creek
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Harvey J Clewell
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
| | - Miyoung Yoon
- The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); ScitoVation, LLC, Research Triangle Park, North Carolina (G.S., X.S., H.J.C., M.Y.); U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (R.N.H.); Medical College of Wisconsin, Milwaukee, Wisconsin (D.G.M.); Centre for Toxicology, University of Surrey, Surrey, United Kingdom (B.G.L.); Science Strategies, LLC, Charlottesville, Virginia (T.G.O.); and Valent USA Corporation, Walnut Creek, California (M.R.C.)
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Ruark CD, Song G, Yoon M, Verner MA, Andersen ME, Clewell HJ, Longnecker MP. Quantitative bias analysis for epidemiological associations of perfluoroalkyl substance serum concentrations and early onset of menopause. Environ Int 2017; 99:245-254. [PMID: 27927583 DOI: 10.1016/j.envint.2016.11.030] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 11/30/2016] [Accepted: 11/30/2016] [Indexed: 05/20/2023]
Abstract
An association between increased serum concentrations of perfluoroalkyl substances (PFAS) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) and early menopause has been reported (Knox et al., 2011; Taylor et al., 2014). This association may be explained by the fact that women who underwent menopause no longer excrete PFAS through menstruation. Our objective was to assess how much of the epidemiologic association between PFAS and altered timing of menopause might be explained by reverse causality. We extended a published population life-stage physiologically-based pharmacokinetic (PBPK) model of PFOS and PFOA characterized by realistic distributions of physiological parameters including age at menopause. We then conducted Monte Carlo simulations to replicate the Taylor population (Taylor et al., 2014) and the Knox population (Knox et al., 2011). The analysis of the simulated data overall showed a pattern of results that was comparable to those reported in epidemiological studies. For example, in the simulated Knox population (ages 42-51) the odds ratio (OR) for menopause in the fifth quintile of PFOA compared to those in the first quintile was 1.33 (95% CI 1.26-1.40), whereas the reported OR was 1.4 (95% CI 1.1-1.8). Using our model structure, a substantial portion of the associations reported can be explained by pharmacokinetics.
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Affiliation(s)
- Christopher D Ruark
- ScitoVation, LLC, RTP, NC, USA; The Hamner Institutes for Health Sciences, RTP, NC, USA; The Procter & Gamble Co., Cincinnati, OH, USA.
| | - Gina Song
- The Hamner Institutes for Health Sciences, RTP, NC, USA.
| | - Miyoung Yoon
- ScitoVation, LLC, RTP, NC, USA; The Hamner Institutes for Health Sciences, RTP, NC, USA.
| | - Marc-André Verner
- Department of Occupational and Environmental Health, Université de Montréal, Montreal, QC, Canada.
| | - Melvin E Andersen
- ScitoVation, LLC, RTP, NC, USA; The Hamner Institutes for Health Sciences, RTP, NC, USA.
| | - Harvey J Clewell
- ScitoVation, LLC, RTP, NC, USA; The Hamner Institutes for Health Sciences, RTP, NC, USA.
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Ramoju SP, Mattison DR, Milton B, McGough D, Shilnikova N, Clewell HJ, Yoon M, Taylor MD, Krewski D, Andersen ME. The application of PBPK models in estimating human brain tissue manganese concentrations. Neurotoxicology 2017; 58:226-237. [PMID: 27989617 DOI: 10.1016/j.neuro.2016.12.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 12/01/2016] [Accepted: 12/01/2016] [Indexed: 01/16/2023]
Affiliation(s)
- Siva P Ramoju
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada.
| | - Donald R Mattison
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada; Samuel R. McLaughlin Centre for Population Health Risk Assessment, Faculty of Medicine, 850 Peter Morand Crescent, Room 119, University of Ottawa, Ottawa, K1G 3Z7, Canada
| | - Brittany Milton
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada
| | - Doreen McGough
- International Manganese Institute, 17 rue Duphot, 75001 Paris, France
| | - Natalia Shilnikova
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada; Samuel R. McLaughlin Centre for Population Health Risk Assessment, Faculty of Medicine, 850 Peter Morand Crescent, Room 119, University of Ottawa, Ottawa, K1G 3Z7, Canada
| | - Harvey J Clewell
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC 27709,United States
| | - Miyoung Yoon
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC 27709,United States
| | - Michael D Taylor
- Nickel Producers Environmental Research Association (NiPERA), 2525 Meridian Parkway, Suite 240, Durham, NC 27713, United States
| | - Daniel Krewski
- Risk Sciences International, 55 Metcalfe Street, Suite 700, K1P 6L5, Ottawa, Canada; Samuel R. McLaughlin Centre for Population Health Risk Assessment, Faculty of Medicine, 850 Peter Morand Crescent, Room 119, University of Ottawa, Ottawa, K1G 3Z7, Canada
| | - Melvin E Andersen
- ScitoVation, 6 Davis Drive, PO Box 110566, Research Triangle Park, NC 27709,United States
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van Eijkeren JCH, Olie JDN, Bradberry SM, Vale JA, de Vries I, Clewell HJ, Meulenbelt J, Hunault CC. Modeling the effect of succimer (DMSA; dimercaptosuccinic acid) chelation therapy in patients poisoned by lead. Clin Toxicol (Phila) 2016; 55:133-141. [DOI: 10.1080/15563650.2016.1263855] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
| | - J. Daniël N. Olie
- National Poisons Information Center, University Medical Center Utrecht, Utrecht, The Netherlands
- Department of Pharmacology and Toxicology, University of Nijmegen, Nijmegen, The Netherlands
| | - Sally M. Bradberry
- City Hospital, National Poisons Information Service (Birmingham Unit), Birmingham, UK
- School of Biosciences, University of Birmingham, Birmingham, UK
| | - J. Allister Vale
- City Hospital, National Poisons Information Service (Birmingham Unit), Birmingham, UK
- School of Biosciences, University of Birmingham, Birmingham, UK
| | - Irma de Vries
- National Poisons Information Center, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Jan Meulenbelt
- National Poisons Information Center, University Medical Center Utrecht, Utrecht, The Netherlands
- Department of Intensive Care Medicine, University Medical Center Utrecht, Utrecht, The Netherlands
- Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, The Netherlands
| | - Claudine C. Hunault
- National Poisons Information Center, University Medical Center Utrecht, Utrecht, The Netherlands
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Song G, Peeples CR, Yoon M, Wu H, Verner MA, Andersen ME, Clewell HJ, Longnecker MP. Pharmacokinetic bias analysis of the epidemiological associations between serum polybrominated diphenyl ether (BDE-47) and timing of menarche. Environ Res 2016; 150:541-548. [PMID: 27429067 DOI: 10.1016/j.envres.2016.07.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Revised: 06/06/2016] [Accepted: 07/03/2016] [Indexed: 06/06/2023]
Abstract
BACKGROUND Associations between serum levels of polybrominated diphenyl ether (PBDE) and timing of pubertal development in adolescent girls (e.g., menarche) have been reported in both a cross-sectional and in a longitudinal study. The associations may be biased by growth dilution and pharmacokinetic changes during pubertal development. OBJECTIVES To use a physiologically-based pharmacokinetic (PBPK) model to assess how much of the epidemiologic association between PBDE and altered timing of menarche might be attributable to growth dilution and pubertal maturation. METHODS We developed a PBPK model of BDE-47, a major congener of PBDE, to perform Monte Carlo (MC) simulation of plasma BDE-47 levels in a hypothetical target population aged 2 to 22 years old. The model used realistic distributions of physiological parameters including timing of growth spurts and menarche. The simulated data were analyzed as if they had come from an epidemiologic study. We compared the results based on the simulated population to those reported. RESULTS The population characteristics, including age and body mass index (BMI) were similar between the simulated and reported groups. In the cross-sectional study design, the association between proportion of subjects with menarche before age 12 years and BDE-47 serum concentration was inverse in our simulated population, whereas the reported association was positive. In the longitudinal study design, simulated data were not suggestive of an association, whereas a delay in pubertal onset with higher concentrations of BDE-47 was observed in the epidemiologic study. CONCLUSION Results of our simulation suggest that in the previous cross-sectional study there was a small negative bias due to pharmacokinetics in the reported relationship between BDE-47 and age at menarche. However, in the longitudinal study there was little evidence of bias. Our study showed how PBPK modeling can be used to quantify the potential bias in epidemiological studies and also suggested that further studies on the optimal approach to modeling exposure are warranted to better understand and quantify the potential bias in the epidemiological associations with BDE-47 due to pharmacokinetics.
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Affiliation(s)
- Gina Song
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
| | - Cody R Peeples
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
| | - Miyoung Yoon
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA.
| | - Huali Wu
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
| | - Marc-André Verner
- Department of Occupational and Environmental Health, Université de Montréal, Canada, and Université de Montréal Public Health Research Institute (IRSPUM), Université de Montréal, Canada
| | - Melvin E Andersen
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
| | - Harvey J Clewell
- The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA
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Pedersen JM, Shim YS, Hans V, Phillips MB, Macdonald JM, Walker G, Andersen ME, Clewell HJ, Yoon M. Fluid Dynamic Modeling to Support the Development of Flow-Based Hepatocyte Culture Systems for Metabolism Studies. Front Bioeng Biotechnol 2016; 4:72. [PMID: 27747210 PMCID: PMC5044513 DOI: 10.3389/fbioe.2016.00072] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 09/05/2016] [Indexed: 11/13/2022] Open
Abstract
Accurate prediction of metabolism is a significant outstanding challenge in toxicology. The best predictions are based on experimental data from in vitro systems using primary hepatocytes. The predictivity of the primary hepatocyte-based culture systems, however, is still limited due to well-known phenotypic instability and rapid decline of metabolic competence within a few hours. Dynamic flow bioreactors for three-dimensional cell cultures are thought to be better at recapitulating tissue microenvironments and show potential to improve in vivo extrapolations of chemical or drug toxicity based on in vitro test results. These more physiologically relevant culture systems hold potential for extending metabolic competence of primary hepatocyte cultures as well. In this investigation, we used computational fluid dynamics to determine the optimal design of a flow-based hepatocyte culture system for evaluating chemical metabolism in vitro. The main design goals were (1) minimization of shear stress experienced by the cells to maximize viability, (2) rapid establishment of a uniform distribution of test compound in the chamber, and (3) delivery of sufficient oxygen to cells to support aerobic respiration. Two commercially available flow devices – RealBio® and QuasiVivo® (QV) – and a custom developed fluidized bed bioreactor were simulated, and turbulence, flow characteristics, test compound distribution, oxygen distribution, and cellular oxygen consumption were analyzed. Experimental results from the bioreactors were used to validate the simulation results. Our results indicate that maintaining adequate oxygen supply is the most important factor to the long-term viability of liver bioreactor cultures. Cell density and system flow patterns were the major determinants of local oxygen concentrations. The experimental results closely corresponded to the in silico predictions. Of the three bioreactors examined in this study, we were able to optimize the experimental conditions for long-term hepatocyte cell culture using the QV bioreactor. This system facilitated the use of low system volumes coupled with higher flow rates. This design supports cellular respiration by increasing oxygen concentrations in the vicinity of the cells and facilitates long-term kinetic studies of low clearance test compounds. These two goals were achieved while simultaneously keeping the shear stress experienced by the cells within acceptable limits.
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Affiliation(s)
- Jenny M Pedersen
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences , Research Triangle Park, NC , USA
| | - Yoo-Sik Shim
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA; ScitoVation, LLC, Research Triangle Park, NC, USA; Joint Department of Biomedical Engineering, University of North Carolina, Chapel Hill, NC, USA
| | - Vaibhav Hans
- Joint Department of Biomedical Engineering, University of North Carolina , Chapel Hill, NC , USA
| | | | - Jeffrey M Macdonald
- Joint Department of Biomedical Engineering, University of North Carolina , Chapel Hill, NC , USA
| | - Glenn Walker
- Joint Department of Biomedical Engineering, North Carolina State University , Raleigh, NC , USA
| | - Melvin E Andersen
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA; ScitoVation, LLC, Research Triangle Park, NC, USA
| | - Harvey J Clewell
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA; ScitoVation, LLC, Research Triangle Park, NC, USA
| | - Miyoung Yoon
- Institute for Chemical Safety Sciences, The Hamner Institutes for Health Sciences, Research Triangle Park, NC, USA; ScitoVation, LLC, Research Triangle Park, NC, USA
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